Welcome
Today’s agenda:
• Take notes,
• Complete activity.
Mr. Coleman
Biology
DNA
• DNA is often called
the blueprint of life.
• In simple terms,
DNA contains the
instructions for
making proteins
within the cell.
Why do we study DNA?
We study DNA for
many reasons, e.g.,
• its central
importance to all
life on Earth,
• medical benefits
such as cures for
diseases,
• better food crops.
Chromosomes and DNA
• Our genes are on
our chromosomes.
• Chromosomes are
made up of a
chemical called
DNA.
The Shape of the Molecule
• DNA is a very
long polymer.
• The basic shape
is like a twisted
ladder or zipper.
• This is called a
double helix.
The Double Helix Molecule
• The DNA double
helix has two
strands twisted
together.
• (In the rest of this
unit we will look
at the structure of
one strand.)
One Strand of DNA
• The backbone of
the molecule is
alternating
phosphate and
deoxyribose, a
sugar, parts.
• The teeth are
nitrogenous
bases.
phosphate
deoxyribose
bases
Nucleotides
O
O -P O
O
O
O -P O
O
One deoxyribose together with its
phosphate and base make a
nucleotide.
O
O -P O
O
Phosphate
Nitrogenous
base
O
C
C
C
O Deoxyribose
One Strand of DNA
nucleotide
• One strand of DNA
is a polymer of
nucleotides.
• One strand of DNA
has many millions
of nucleotides.
Four nitrogenous bases
DNA has four different bases:
• Cytosine
C
• Thymine T
• Adenine A
• Guanine G
Two Kinds of Bases in DNA
• Pyrimidines are
single ring bases.
• Purines are double
ring bases.
N C
O C
N
C
N C
N
N C
C
C
N
N C
N C
Thymine and Cytosine are
pyrimidines
• Thymine and cytosine each have one
ring of carbon and nitrogen atoms.
N
O
N
O
C
C C
N
N
C
C
thymine
O
C
C
C
N
C
cytosine
Adenine and Guanine are
purines
• Adenine and guanine each have two
rings of carbon and nitrogen atoms.
O
N
N
C
N
C
N
C
C
C
C
N
N
N
C
Adenine
N
C
N
C
Guanine
N
C
Two Stranded DNA
• Remember, DNA
has two strands
that fit together
something like a
zipper.
• The teeth are the
nitrogenous bases
but why do they
stick together?
N
N
C
N
N
C
C
C
O
• The bases attract each
other because of
hydrogen bonds.
• Hydrogen bonds are
weak but there are
millions and millions
of them in a single
molecule of DNA.
• (The bonds between
cytosine and guanine
are shown here.)
C
N
Hydrogen Bonds
N
C
N
C
C
C
N
O
Hydrogen Bonds, cont.
• When making
hydrogen bonds,
cytosine always pairs
up with guanine,
• And adenine always
pairs up with
thymine.
• (Adenine and thymine
are shown here.)
O
N
O
C
C
C C
N
C
Important:
• Adenine and Thymine always join
together
A T
• Cytosine and Guanine always join
together
C G
DNA by the numbers
• Each cell has about 2 m
of DNA.
• The average human has
75 trillion cells.
• The average human has
enough DNA to go from
the earth to the sun
more than 400 times.
• DNA has a diameter of
only 0.000000002 m.
The earth is 150 billion m
or 93 million miles from
the sun.
Thank You